A More Important Role for the Ozone‐S(IV) Oxidation Pathway Due to Decreasing Acidity in Clouds,Journal of Geophysical Research: Atmospheres

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A More Important Role for the Ozone‐S(IV) Oxidation Pathway Due to Decreasing Acidity in Clouds
Journal of Geophysical Research: Atmospheres ( IF 3.8 ) Pub Date : 2020-09-09 , DOI: 10.1029/2020jd033220
Jiarong Li ₁ , Chao Zhu ₁ , Hui Chen ₁ , Hongbo Fu ₁ , Hang Xiao ₂ , Xiaofei Wang ₁ , Hartmut Herrmann _{1,

3,

4} , Jianmin Chen _{1,

2,

5}

Affiliation

Clouds significantly affect the Earth's radiation budget and play a critical role in atmospheric sulfate formation. The pathways of S(IV) oxidations have recently caused a controversial attention under severe haze episodes due to the variable acidity and water content in aerosol particles. In this study, a total of 158 cloud samples were collected from 2014 to 2018 at the summit of Mt. Tai, China, to explore the roles of atmospheric oxidants in aqueous S(IV) oxidation. The results showed that the averaged pH value of cloud water increased dramatically from 3.86 (Guo et al., 2012, https://doi.org/10.1016/j.atmosenv.2012.07.016) in 2007–2008, ~5.5 in 2014, to ~6.4 in 2018, respectively, while water soluble secondary ions (SO₄²⁻, NO₃⁻ and NH₄⁺) and S(IV) decreased significantly. The four pathways of S(IV) oxidation by O₃, H₂O₂, NO₂, and trace metal‐catalyzed autooxidation were further discussed, and the roles in S(IV) oxidation pathways were found changing significantly with pH value in clouds. The rate of H₂O₂ pathway contributed about 95.8% for S(IV) oxidation when pH was less than 4.0. For pH around 5.0, the rate of O₃ pathway became comparable with the H₂O₂ pathway, and it accounted more than 95.2% for the total S(IV) oxidation rate when pH was larger than 6.0. Based on the long‐term field measurement, this study indicated that the high concentration of O₃ and the increasing trend of pH promoted a shift of the dominant S(IV) oxidation from H₂O₂ pathway in a previous study (Shen et al., 2012, https://doi.org/10.1016/j.atmosenv.2012.07.079) to O₃ pathway in clouds.

更新日期：2020-09-20

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